Air moving apparatus (e.g., electric fans), appliances including a motor, or devices including electric heating elements are potentially subject to electrical problems due to accident, misuse, excessive moisture and/or heat, which can cause the wiring in a motor, the cord set, or other wires to short. Motors in appliances often incorporate a thermal cut-off device which reacts to an increase in heat to shut off the motor. Thermal devices are generally slow acting and designed to sense and react to a gradual heat increase. The heat increase can be caused by a variety of factors such as a slow acting short in the motor windings, or a bearing failure resulting in reduced air flow. Such factors may cause the winding temperature to rise.
Thermal devices are most effective at sensing localized heating, and as such, if a failure occurs at a location remote from the thermal device, the thermal device may not sense the condition quickly enough to shut the motor down prior to failure. As such, rapidly acting remote failures may result in damage to the electric device (i.e., the electrical apparatus) before the thermal device operates.
Faults that occur in appliances and electrical devices produce heat by friction, arcing, and resistive heating. The faults, and thus the sources, may occur in combination. For example, in an appliance or electrical device that utilizes an electric motor, frictional heating acts to cause bearing failure. Bearing failure acts to cause rotor lockup, and rotor lockup acts to cause inductive heating. The inductive heating breaks down insulation and causes arcing.
A properly sized circuit interrupter (e.g., a fuse) will react to rapid failure conditions and/or an increase in current over its capacity. Such a circuit interrupter will protect components upstream from the motor, such as the cord set. A circuit interrupter will also react to shorts internal to the switch, lead wires, and motor windings. A circuit interrupter, to be effective, should preferably be non-replaceable in order to insure that the user does not defeat the purpose of the circuit interrupter, which is to enhance safety of the thermal cut-off device thus preventing damage to components, the apparatus, or the appliance. In addition, the combination of these two devices (i.e., the thermal device and the circuit interrupter) in an electrical apparatus or appliance will further enhance the safety of the apparatus or appliance as well as act to protect its components.